The present invention relates generally to geomembranes and, more particularly, to a multilayered coextruded geomembrane constructed from selected polyethylene resins. The invention achieves a unique combination of performance characteristics which greatly enhances the efficacy of the geomembrane in the field.
With the ever increasing desire in recent years to protect the environment, there has arisen a demand for sheet materials which can effectively seal large landfills and hazardous material sites from the surrounding land and water. Such sheet material, commonly designated as a "geomembrane", must be strong, chemically resistant, flexible and effectively assembled into a very large continuous sheet in the field. One method of assembly now used is heat bonding of adjacent edges of the individual sheets, which are typically up to 34 feet wide and perhaps hundreds of yards in length. Therefore, weldability is also important for all types of geomembranes.
High density polyethylene geomembranes have good overall strength including seam strength and are very resistant to attack by chemicals. Limitations of high density polyethylene geomembranes include low flexibility, a functionally limited elongation range and susceptibility to stress cracking if improperly installed. On the other hand, very low density polyethylene geomembranes are much more pliable than high density polyethylene and have an excellent functional elongation range allowing the material to conform to irregular surfaces or changes in the subgrade. However, very low density polyethylene is less chemically resistant and has a lower seam strength than high density polyethylene when tested in accordance with standard seam peel and shear tests.
Accordingly, a need exists for a geomembrane sheet material which not only exhibits exceptional seam or weld strength, but also has a greater degree of flexibility and an ability to conform to irregularities in its supporting surface.